Host processor systems may store and retrieve data using storage devices containing a plurality of host interface units (host adapters), disk drives, and disk interface units (disk adapters). Such storage devices are provided, for example, by EMC Corporation of Hopkinton, Mass. and disclosed in U.S. Pat. Nos. 5,206,939 to Yanai et al., 5,778,394 to Galtzur et al., U.S. Pat. No. 5,845,147 to Vishlitzky et al., and U.S. Pat. No. 5,857,208 to Ofek, which are incorporated herein by reference. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels of the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical volumes. Different sections of the logical volumes may or may not correspond to the actual disk drives.
Data striping is a technique of segmenting logically sequential data so that segments can be assigned to multiple disk drives or other physical devices in a round-robin fashion and thus written concurrently. Data striping may be used in connection with RAID (redundant array of independent disks) storage systems and may be useful in situations where a processor is capable of reading or writing data faster than a single disk can supply or accept it. Specifically, in connection with accessing data that has been striped, while one data segment is being transferred from the first disk, a second disk can locate the next segment. Known management systems allow for the adjustment of the coarseness of the striping pattern and data striping may be used separately from or in conjunction with data mirroring techniques. Advantages of striping include improvements in performance and throughput.
In a storage system using data striping, a problem may occur concerning the unbalanced distribution of new data written to a virtualized storage pool of storage devices having logical volumes that map to physical storage areas. When new empty devices are added to an existing storage pool in which data is evenly striped across all pool members, as the older devices begin to approach 100% utilization, new data written to the pool is no longer able to be widely striped across all the pool members and instead becomes restricted to the new, less-utilized pool members.
Accordingly, it would be desirable to provide a system that may advantageously facilitate the normalization of utilized capacities of members of a storage pool in response to conditions of the storage pool.